1. Field of the Invention
The present invention relates to a plasma display apparatus, and more particularly, to a plasma display apparatus in which brightness and discharge efficiency are enhanced by using a space voltage in a discharge cell and a driving method thereof.
2. Description of the Background Art
A plasma display apparatus is included of a front substrate, a rear substrate, and discharge cells formed between the front substrate and the rear substrate. Further, the plasma display apparatus displays an image by exciting phosphors by vacuum ultraviolet rays, generated when an inert gas in discharge cells is discharged clue to a high voltage.
FIG. 1 is an exploded perspective view illustrating a structure of a discharge cell of a surface discharge type AC plasma display panel.
The surface discharge type AC plasma display panel is manufactured by forming a plurality of films on two flat glass substrates serving as an upper substrate 10 and a lower substrate 20 and bonding the two flat glass substrates to each other. The upper substrate 10 and the lower substrate 20 are arranged to face each other. Scan electrodes Y and sustain electrodes Z are formed on the upper substrate 10 and address electrodes X are formed on the lower substrate 20.
Each of scan electrodes Y is included of a transparent electrode 12Y and a metal bus electrode 13Y having a narrower width than the transparent electrode 12Y, and each of sustain electrodes Z is included of a transparent electrode 12Z and a metal bus electrode 13Z having a narrower width than the transparent electrode 12Z. An upper dielectric layer 14 and a protective layer 16 are stacked on the upper substrate 10 so as to cover the scan electrodes Y and the sustain electrodes Z. Wall charges generated during plasma discharging are accumulated on the upper dielectric layer 14. The protective layer 16 acts to prevent the sputtering occurring during the plasma discharging causing damage to the upper dielectric layer 14, and to enhance emission efficiency of secondary electrons.
The lower substrate 20 is covered with a lower dielectric layer 22, and barrier ribs 24 are formed on the lower dielectric layer in order to prevent UV rays and visible light rays generated in a discharge cell by the discharging leaking into adjacent discharge cells. The lower dielectric layer 22 and the barrier ribs 24 are covered with a phosphor 26. The phosphor 26 is excited by UV rays generated during the plasma discharging, thereby emitting a color of visible light rays among red, green and blue.
FIG. 2 illustrates voltage waveforms of driving pulses for driving a plasma display panel in a time divisional manner, in which one frame is divided into a plurality of sub-fields. The plasma display panel is generally driven in a time divisional manner by dividing a single frame into a plurality of sub-fields, during which different numbers of discharge operations are caused, in order to express a gray level. Each subfield is divided into a reset period for initializing all discharge cells, an address period for selecting a scan line and discharge cells to be discharged among discharge cells connected to the selected scan line, and a sustain period for expressing the gray level according to the number of discharge operations.
For example, in case that the image is displayed in 256 gray levels, one frame period (16.67 ms) corresponding to 1/60 second is divided into eight sub-fields SF1 to SF8 as shown in FIG. 2. Each of the sub-fields SF1 to SF7 is divided into a reset period, an address period and a sustain period.
The reset period and the address period are the same for each sub-field. However, the sustain period and the number of sustain pulses applied to electrodes in the sustain period are different and increase in a ratio of 2n (n=0, 1, 2, 3, 4, 5, 6, 7) for each sub-field. In this way, since the sustain periods of the sub-fields for implementing the gray level according to the number of discharge operations are different for each sub-field, it is possible to express a gray level by the sub-fields, and is possible to display a single image frame by the combination of the sub-fields.
FIG. 3 is a voltage waveform of sustain pulses applied to electrodes in a sustain period. One period of sustain pulses includes an energy recovery up time (ER_up time), a sustain up time (Sus_up time), and an energy recovery down time (ER_down time).
As described above, according to the conventional driving method of a plasma display apparatus, the waveform of sustain pulses applied to electrodes in the sustain period is fixed. That is, the energy recovery up time, the energy recovery down time, and the sustain up time during a single period of sustain pulses do not vary.